Exploitation of the cellulase enzyme complex of neurospora

Abstract

The invention relates to the gene encoding the enzyme cellobiohydrolase-1. Specifically, the invention concerns the elucidation of the regulatable promoter sequence of said gene and the subsequent genetic manipulation of said sequence so as to combine it with DNA sequence structure of a heterologous peptide in order to provide for selective expression of heterologous peptide in accordance with the expression features of the promoter.

We claim: 
     
       1. A method of purifying a fusion protein containing a heterologous protein comprising: (a) transforming a host cell with an expression cassette encoding a fusion protein, wherein the fusion protein contains a C-terminal cellulose binding domain of a Neurospora crassa cellobiohydrolase-1, a linking region, and a heterologous protein; wherein the C-terminal cellulose binding domain of cellobiohydrolase-1 and the heterologous protein are linked together by the linking region; and wherein the host cell expresses the fusion protein;   (b) contacting the fusion protein with a cellulose matrix; wherein the fusion protein binds to the cellulose matrix;   (c) washing the cellulose matrix; and   (d) eluting the fusion protein from the cellulose matrix; wherein the fusion protein is purified.   
     
     
       2. A method of purifying a heterologous protein comprising: (a) transforming a host cell with an expression cassette encoding a fusion protein wherein the fusion protein contains a C-terminal cellulose binding domain of a Neurospora crassa cellobiohydrolase-1, a linking region, and a heterologous protein; wherein the C-terminal cellulose binding domain of cellobiohydrolase-1 and the heterologous protein are linked together by the linking region; wherein the linking region contains a specific proteolytic cleavage site; and wherein the host cell expresses the fusion protein;   (b) contacting the fusion protein with a cellulose matrix; wherein the fusion protein binds to the cellulose matrix;   (c) washing the cellulose matrix; and   (d) contacting the specific proteolytic cleavage site with a proteolytic protein that specifically recognizes the specific proteolytic cleavage site, and therein releases the heterologous protein from the cellulose matrix; wherein the heterologous protein is purified.   
     
     
       3. A method of immobilizing a heterologous protein on a cellulose matrix comprising contacting a fusion protein containing a C-terminal cellulose binding domain of a Neurospora crassa cellobiohydrolase-1, and a heterologous protein with a cellulose matrix; wherein the heterologous protein is immobilized on the cellulose matrix. 
     
     
       4. A method of using the immobilized heterologous protein of claim 3 as a biocatalyst comprising: (a) contacting a substrate for the heterologous protein with the immobilized heterologous protein; and   (b) collecting the product.